Studies on a radioimmunoassay for human erythopoietin.

A highly purified erythropoietin (ESF) preparation (12,000 units per milligram of protein) was labeled with Na'125I using the Chloramine-T method. Undamaged immunoreative labeled ESF was separated from the damaged, nonimmunologically receiveESF by Sephadex G-150 fractionation. This undamaged immunreactive ESF was usedin radioimmunoassay for human erythropoietin. Separation of bound from free antigen was acheived using the double-antibody technique. Approximately 55 per cent binding wasobserved at an antiserum dilution of 1:1500. This assay appears to be sensitive enough to detect as little as 0.025 milliunits of the International Reference Preparation erythropoietin. The estimated levels of thid hormone in normal and anemic uremic human subjects suggests that immunoreactive serum erythropoietin levels are elevated above normal in anemia of uremia.